Solvent-free synthesis of PEO/garnet composite electrolyte for high-safety all-solid-state lithium batteries

Solid electrolyte membrane plays a vital role in the application of all-solid-state batteries. In this paper, composite electrolyte membranes incorporating commercial submicron Li6.75La3Zr1.75Ta0.25O12 (LLZTO) are prepared by solvent-free hot rolling method. It is found that the addition of LLZTO to the PEO-LiTFSI-based electrolyte can effectively reduce the crystallinity of PEO, improve the ion conductivity, voltage window, mechanical properties and interfacial stability of the composite solid electrolyte membrane. The composite electrolyte membrane with the optimal LLZTO content of 10 wt% exhibits a maximum ionic conductivity of 3.03 × 10−4 S cm−1 at 55 °C and a maximum elongation break of 74.8%. And also, the lithium symmetric cell assembled with 10 wt% LLZTO membrane exhibits the lowest polarization voltage and the best cycle performance, which can be attributed to the enhanced mechanical properties of the membrane and the lower and stable interfacial resistance between the membrane and lithium metal. The all-solid-state LiFePO4/Li batterie delivers a high specific capacity of 155.8 mAh g−1 at 0.1C rate at 55 °C, and exhibits excellent cycle performance and rate performance. In addition, the pouch cells assembled with PEO-LiTFSI-10LLZTO composite electrolyte membrane can still maintain the pristine voltage of 3.39 V and power light-emitting diodes (LEDs) under harsh conditions such as cutting, showing an excellent safety performance.